Time shift: How to make EV charging as clean as possible

WattTime data helps EVs charge with lower-carbon power. But the rates and incentives to encourage these cleaner choices are still being developed.
By Jeff St. John

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Vic Shao, CEO of Amply, sees a couple of different ways that his company can help transit agencies and commercial fleet operators charge their electric vehicles with the lowest-carbon electricity possible.

One is to buy enough renewable energy credits to supply 100 percent carbon-free power on an annual basis, as Amply now offers its California customers. That’s the standard way for corporations to achieve 100 percent clean energy — at least on paper.

The new way is to adjust the time of day when EVs are charged to match the time of day when the largest amount of clean energy is available, using data on the relative carbon-intensity of the actual power grids that EVs are connected to on an hour-to-hour basis. Last week, Amply announced plans to start offering this tool to its EV-charging-as-a-service customers — akin to the more aggressive decarbonization approaches being pioneered by companies including Google and Microsoft.

The data for this effort is coming from WattTime, a startup that pulls data from power plants and energy markets to assess the emissions profiles of power grids around the world. Besides providing snapshots of the mix of clean versus dirty power at any time, it predicts when EV chargers can increase their utilization of solar and wind power or avoid triggering fossil-fueled peaker plants to be fired up.

In terms of accounting for the emissions impact of EV charging, getting it down to the hourly level, and accounting for different power plant usage, is as good as it gets,” Shao said. A lot of our large enterprise customers have larger sustainability goals. Having that real-time data and reports validating that is really important for them.”

What this system doesn’t yet offer, at least yet, is a specific link between using cleaner power to charge EVs and how much those customers pay for that electricity. There’s not an exact mechanism for pricing in the actual hourly emissions,” Shao said.

But with California and many other states pushing to decarbonize their power grids to combat climate change, having that data, first and foremost, is the start of that conversation.”

Shifting when EVs are charged can make a big difference in emissions

WattTime, a subsidiary of nonprofit research organization RMI, has spent the past seven years building increasingly sophisticated methods of collecting, analyzing and sharing marginal emissions data. Its Automated Emissions Reduction technology is informing a host of grid operations, from state-incentivized battery systems in California to demand response providers’ behind-the-meter load controls. (Canary Media is an independent affiliate of RMI.)

But EV charging was one of WattTime’s first commercial applications, through a 2015 partnership with eMotorWerks, the maker of JuiceBox chargers that has since been acquired by Enel X and integrated into that company’s broader distributed energy services offering.

JuiceNet Green is what Enel X now calls this option for customers to tap the cleanest possible electricity for their daily EV charging routines. In simple terms, it overlays an emissions value on the prices they pay for hour-to-hour charging, allowing them to automate when charging sessions start and end accordingly.

They can effectively take in the WattTime emissions signal and build a strategy around that,” Laura Corso, WattTime’s managing director of partnerships, told Canary Media. That can include a virtualized pricing element tied to the intensity of the emissions, as well as settings that defer charging to periods when forecasts and real-time data indicate that the share of clean power on the grid will peak.

The most important factor for EV charging is making sure cars are topped off and ready to drive when people need them, she emphasized. Drivers can always interrupt the automated settings to get the charge they need by the time they need it. Within those limits, however, letting the system adjust charging can yield significant emissions benefits.

In a 2019 study, WattTime estimated that applying its emissions data to EV charging can reduce associated emissions by about 20 percent on an annual basis. That differential can grow to as high as 90 percent on certain days, such as sunny, mild days in California when solar power is flooding the grid.

On some grids, the cleanest power is available at nighttime, when demand is low and when wind power tends to be the most productive. Since most people have until the morning to top off their EVs, that’s a predictable window in which to alter charging patterns to take advantage of periods with lower emissions profiles, as this chart of Enel X JuiceNet Green data indicates.

Of course, individual results rely greatly on how much clean versus dirty power is available on the grid in question, as well as how much those emissions rates vary throughout the day. But even if it’s an average of 2 to 5 percent over the course of a few months, it’s better than nothing,” Corso said — and in some cases, the difference can be quite dramatic.

Take this graph representing a typical California energy mix, with lots of solar power at midday, followed by a drop-off in solar and consequent ramp-up of natural-gas power plants in the evening. The clear lesson here is to avoid charging during those peak evening hours, an imperative already built into the time-of-use pricing rates in place in the state.

But delaying a midday charge by a few hours can also make a lot of difference, said Joseph Vellone, head of the North America division for EV charging software provider ev.energy. That’s what the company learned in the GridShift pilot project with Silicon Valley Clean Energy, a California community choice aggregator that signed up customers willing to turn over control of when their cars are charged in exchange for up to $10 a month in bill credits.

The rollout of the program coincided with the Covid-19 pandemic, leaving many participants working from home and driving a lot less, he said. Those traditional working hours coincide with times of excess solar generation on the grid. WattTime’s data allowed ev.energy to predict when pushing EV charging later into the day could significantly increase the amount of renewable power they were using.

Most people are inclined to charge their EVs as soon as possible, but the pilot project nudged them to specify the time by which they needed a full charge, which allowed for much charging to be completed later in the day when renewable power was plentiful, Vellone said. The chart below indicates the emissions savings this was able to achieve.

We’re doing this with residential charging right now, but there’s no reason we couldn’t apply the same thing to workplace charging,” which entails a lot of drivers plugging in their cars during the day, he said. Folks are typically plugged in at least eight hours at the office, and require typically two to three hours of charge,” offering a relatively wide window for shifting charging patterns.

This kind of data can inform future EV charging plans as well as manage existing chargers, Corso noted. WattTime is collaborating with utility Ameren Missouri to apply its data to an EV charging incentive program being considered by regulators in the state. The goal is to determine if WattTime’s Automated Emissions Reduction technology can provide an emissions reduction benefit that’s deserving of a special incentive to reward customers for shifting their charging to times when more clean power is available.

Getting paid for cleaner charging: A work in progress

Whether people can get paid for managing the intensity of their marginal emissions is another matter, however.

Sometimes dirtier grid power is also more expensive power, as with that supplied by peaker plants to meet moments of peak electricity demand. In those instances, pricing that discourages on-peak consumption, like the rates offered by an increasing number of utilities and state regulators, could yield the same impact as following emissions signals.

At other times, that link between cost and cleanliness is less clear. California’s surplus of solar power can drive low or even negative prices on its wholesale energy markets and is leading to increasing curtailment of solar in excess of demand. But the retail rates that customers pay don’t yet account for those drastic shifts in wholesale prices, Corso said.

Real-time wholesale energy market prices tend to track the renewable vs. fossil fuel share of power on grids more closely, but not always. Many grids also share a cheap and clean” linkage between off-peak nighttime electricity rates and wind power production, for example. But these nighttime hours may also be served by baseload coal-fired power, the dirtiest kind there is.

Could there be any sort of emissions-based rate design when it comes to utilities or state regulators? The answer is, we don’t know — but it’s something we’ve seen utilities and regulators start to talk about,” Corso said.

Enel X is also interested in opportunities to add economic incentives to the growing consumer, utility and fleet interest” in the JuiceNet Green feature supported by WattTime’s data, said Giovanni Bertolino, head of e-mobility at Enel X North America. We believe there is still a lot of untapped potential for optimizing charging across customer segments to reduce emissions.”

Amply’s Vic Shao pointed out that California’s Low Carbon Fuel Standard, a significant source of incentives for expanding EV charging in the state, already rewards chargers that use on-site solar power. Integrating the marginal emissions impact of charging at different times of the day could be a route to tying economic value to these decisions by EV owners, he said.

Finding a way to price emissions into electricity rates and incentive structures will be an important step in informing the gigantic optimization problem” that fleet EV charging represents, Shao said.

The most important criteria is no interruptions from transitioning from fossil fuel to electric. It’s got to be seamless,” he said. Priority No. 2 is cost. They want to have a handle on pricing. […] Beyond that are existing sustainability and environmental [goals].”

Which of these criteria are the most important to you? Is it time and reliability? Is it pricing and cost? Is it emissions? Is it sustainability?” Shao asked. I think the economics will just have to lead the industry in the right direction.”

(Lead image: Andrew Roberts)

Jeff St. John is director of news and special projects at Canary Media. He covers innovative grid technologies, rooftop solar and batteries, clean hydrogen, EV charging and more.